Air bag door with tear seam

Abstract

A cover (10) of integral construction for an air bag comprising: a panel (20) and a hinge (26) formed in a first side (28) of the cover (10) for enabling the panel to rotate thereabout after the panel separates from a seam on the opposite side of the panel in response to forces imparted thereto by an expanding air bag. The seam includes stress enhancing features for increasing stresses in the material causing same to tear and separate. These stress enhancing features includes a laterally extending narrow first portion (42), a closely spaced laterally extending narrow second portion (44) and a thin bridge (46) joining the first and second portions (42,44). The first portion, second portion and bridge are relatively movable one to the other so as to generate in the material at least two zones of increased tensile stress and at least two zones of increased compressive stress sufficient to cause the material to tear.

We claim: 
     
       1. A cover (10) of integral construction for an air bag comprising: a panel (20); hinge means (26) formed adjacent a first side (28) of the panel for enabling the panel to rotate thereabout after the panel separates from a seam means in response to forces imparted thereto by an expanding air bag,   the seam means (40), interposing an opposite side (32) of the panel, for providing a tear or crack region to permit the panel to separate at the opposite side (32), comprising stress enhancing means for increasing stresses including   a narrow first portion (42), a closely spaced narrow second portion (44) and a thin bridge (46) joining the first and second portions (42,44) formed in material forming the seam means, the first portion, second portion and bridge are relatively rotatably movable one to the other so as to generate in the material at least two zones of increased tensile stress a first zone of increased tensile stress generally between the first portion (42) and the thin bridge (46) and a second zone of increased tensile stress generally between the second portion and the thin bridge (46) and a zone of compressive stress, on an opposite side of the first and second portion generally opposite each zone of increased tensile stress.   
     
     
       2. The cover (10) as defined in claim 1 wherein in response to inflation forces imparted by the air bag the cover (10) is placed in a stressed condition, causing the relative rotation of the first portion (42), bridge (46) and second portion (44) thereby stretching the material forming the seam means to its ultimate elongation to produce the zones of increased tensile stress, causing such material to initially tear or crack and in response to the continued inflation of the air bag to cause the crack to propogate, severing the panel (20) at the opposite side (32). 
     
     
       3. A cover (10) of integral construction for an air bag comprising: a panel (20); hinge means (26) formed adjacent a first side (28) of the panel for enabling the panel to rotate thereabout after the panel separates from a seam means in response to forces imparted thereto by an expanding air bar,   the seam means (40), interposing an opposite side (32) of the panel, for providing a tear or crack region to permit the panel to separate at the opposite side (32), comprising stress enhancing means for increasing stresses including   a narrow first portion (42), a closely spaced narrow second portion (44) and a thin bridge (46) joining the first and second portions (42,44) formed in material forming the seam means, the first portion, second portion and bridge are relatively rotatably movable one to the other so as to generate in the material at least two zones of increased tensile stress, the first zone generally between the first portion (42) and the thin bridge (46) and a second zone generally between the second portion and the thin bridge (46) wherein in response to inflation fores imparted by the air bag the seam means is placed in a condition of increased stress stretching the first portion, bridge and second portion apart and causing the first portion and bridge to rotate relative to one another and the second portion and bridge to rotate relative to one another to generate the first and second zones of increased tensile stress.   
     
     
       4. A cover (10) of integral construction for an air bag comprising: a panel (20); hinge means (26) formed adjacent a first side (28) of the panel for enabling the panel to rotate thereabout after the panel separates from a seam means in response to forces imparted thereto by an expanding air bag,   the seam means (40), interposing an opposite side (32) of the panel, for providing a tear or crack region to permit the panel to separate at the opposite side (32), comprising stress enhancing means for increasing stresses including   a narrow first portion (42), a closely spaced narrow second portion (44) and a thin bridge (46) joining the first and second portions (42,44) formed in material forming the seam means, the first portion, second portion and bridge are relatively rotatably movable one to the other so as to generate in the material at least two zones of increased tensile stress, the first zone generally between the first portion (42) and the thin bridge (46) and a second zone generally between the second portion (44) and the thin bridge (46), wherein in response to inflation forces imparted by the air bag the cover (10) is placed in a stressed condition, causing the relative rotation of the first portion (42), bridge (46) and second portion (44) thereby stretching the material forming the seam means to its ultimate elongation to produce the zones of increased tensile stress, causing such material to initially separate or crack and in response to the continued inflation of the air bag to cause the crack to propagate, severing the panel (20) from the opposite side (32) wherein a zone of compressive stress is generated generally opposite each zone of increased tensile stress in portions of the material compressed in response to the relative rotation of the first portion, second portion and bridge.   
     
     
       5. The cover as defined in claim 4 wherein the cover is mounted on the top of an instrument panel proximate a windshield of a vehicle such that the cover is subject to sun loanding and wherein the material defining the cover exhibits a flexural modulus of approximately 240K psi such that the structural properties of the cover are not substantially reduced due to increased temperatures arising at the sun loading. 
     
     
       6. The cover as defined in claim 4 wherein the ultimate elongation of the material is between 200 percent and 500 percent. 
     
     
       7. The cover as defined in claim 4 wherein at least one of the first and second portions (42,44) comprises a sharp edged groove. 
     
     
       8. The cover as defined in claim 4 wherein the first and second portions includes a sharp edged groove, wherein the interior portion of each groove is oppositely oriented. 
     
     
       9. The cover as defined in claim 8 wherein the material is stretched to its ultimate elongation in the vicinity of the interior of at least one of the grooves. 
     
     
       10. A cover (10) for an air bag (34) comprising: a panel (20) and an integrally formed seam means (40) along one side of the panel;   the seam means comprising:   a first rear surface (62) and a parallel spaced second rear surface (64), a rear transition surface (66) joining the first rear and second rear surfaces, a first front surface (70) spaced from the first rear surface and rear transition surface, a first front transition surface (72) extending from the first front surface (70) toward the second rear surface (64) and a second front transition surface (74) extending forwardly from generally proximate an inner edge (76) of the first front transition surface (72), wherein as the air bag expands it exerts an expansion force on the cover which tends to stretch the material forming the seam means (40) such that a first zone of increased tensile stress is created in the vicinity of the inner edge (76) of the first front transition surface (72) and wherein a first zone of increased compressive stress is created generally in the second rear surface (64) and wherein a second zone of increased tensile stress is created along the intersection of the rear transition surface (66) and first rear surface (62) and a second zone of increased compressive stress is created generally about the intersection of the first front surface (70) and first front transition surface (72), such increased tensile and compressive stresses cooperating to cause the material forming the seam means to stretch to its ultimate elongation and tear thereby separating the panel from the seam means.   
     
     
       11. The cover as defined in claim 10 wherein the vicinity of the intersection of the rear transition (66) and first rear surface (70) the first front surface (62) is generally angularly spaced from the rear transition surface by approximately 90 degrees. 
     
     
       12. The cover as defined in claim 11 wherein the angular spacing is 89 degrees. 
     
     
       13. The cover as defined in claim 10 wherein in the vicinity of the intersection of the rear transition (66) and first rear surface (62) the first rear surface (62) is generally angularly spaced from the rear transition surface by approximately 60 degrees. 
     
     
       14. The cover as defined in claim 13 wherein the angular spacing is 61 degrees. 
     
     
       15. The cover as defined in claim 13 wherein in the first front transition surface extends inwardly at an angle relative to the first rear surface of approximately 90 degrees. 
     
     
       16. The cover as defined in claim 15 wherein an intersection line (76) between the first and second transition surfaces is closely spaced from the second rear surface (64) to generate a zone of increased tensile stress as the seam means is expanded. 
     
     
       17. The cover as defined in claim 16 wherein the spacing is approximately 0.5 mm. 
     
     
       18. The cover as defined in claim 16 wherein the distance from the first front transition surface (72) to the intersection of the first rear surface (62) and rear transition surface (66) is spaced to generate a second zone of increased tensile stresses as the seam means is expanded. 
     
     
       19. The cover as defined in claim 18 wherein the distance is approximately 0.5 mm.